The present invention concerns voltage-controlled oscillators, particularly voltage-controlled oscillators used to facilitate communications between electronic devices or circuits.
Today there are a wide variety of computer and telecommunications devices, such as personal computers (PCs), mobile telephones, and personal data assistants (PDAs), that need to share information with each other. Generally, this information is communicated from a sending device to a receiving device.
The sending device generally has the data in the initial form of a set of digital words (sets of ones and zeros). In the sending device, a transmitter circuit converts each word into a sequence of electrical pulses, with each pulse timed according to a data clock, and transmits the timed sequence of pulses through a cable, circuit board, or other medium to the receiving device. The receiving device includes a receiver circuit that first determines the timing of the pulses and then identifies each of the pulses in the signal as a one or zero, enabling it to reconstruct the original digital words.
A key component in both the transmitter and the receiver is a voltage-controlled oscillatorxe2x80x94a circuit that produces a signal that varies back and forth between two voltage levels at a frequency based on an input control voltage. The transmitter uses a VCO to place digital information into a high-frequency carrier signal, and the receiver uses a VCO to separate the digital information from the high-frequency carrier signal. Thus, reliable and precise VCO operation is critical to transmission and reception of digital information.
One problem the present inventors identified in conventional VCOs is the use of single-ended control voltages. In other words, conventional VCOs include only one input point for receiving a control voltage. The single-ended control voltage forces VCO oscillation frequencies to deviate randomly from desired frequencies in response to unintended, yet inevitable, variations in the control voltage (or power-supply voltages relative to the control voltage.) For example, for a transmitter VCO intended to produce an oscillation frequency of 2.4 Gigahertz (2.4 billion oscillations per second), control-voltage variations, stemming from inevitable power-supply fluctuations, may cause the frequency to vary from 2.4001 Gigahertz to 2.3992 Gigahertz to 2.4010 Gigahertz. Similarly, a receiver VCO frequency will also vary based on its own local control voltage. Such frequency deviations can make it more difficult to reliably communicate data between electronic devices.
Accordingly, there is a need for better voltage-controlled oscillators.
To address these and other needs, the present inventors devised an exemplary voltage-controlled oscillator (VCO) circuit that includes two frequency-control inputs and a differentially tunable impedance that varies according to the voltage difference F between the frequency-control inputs. The differentially tunable impedance rejects noise (undesirable voltage variations) common to both of the frequency-control inputs and thus provides the VCO with a noise immunity, known as common-mode rejection, that is not available in conventional VCOs with single control inputs.
Other aspects of the invention include phase-lock loops, receivers, transmitters, and transceivers that incorporate the exemplary VCO. Additionally, various embodiments of the invention comply with Bluetooth and/or other wireless communications standards.